Hi Marckitt,
So far, I have been lucky to not ever have any snakes with respiratory infections and I have never treated one. So, take what I say with a grain of salt. But, from everything I have read and seen in videos it sounds to me like he has a respiratory infection. Have you noticed any bubbles coming out of his nostrils when he breaths? The vet may have said antibiotics aren't necessary, but it might not be a bad idea to give him a few of the steam treatments I posted videos for in your other thread about this. I'm curious, are the sides of his tub ever steamed up with condensed water sitting on the sides? If so, you don't have enough ventilation/airflow, which can definitely cause respiratory infections. If you are using newspaper for substrate, I would recommend not keeping it soak and wet 24/7. Personally, I switched from generous daily misting with luke warm water to misting only moderately daily and sometimes only every other day. I try not to soak the whole bottom of the tub when I mist, either. I have other wadded up pieces of newspaper, as well as one single sheet of newspaper, which is laid over top of everything, so I try to just mist those down. The actual humidity is more important than the dampness. I also increased my ventilation significantly in the tubs and I also leave the ceiling fan running on medium in my snake room. So, basically, all of the newspaper dries within a few hours. That's how I gauge whether or not there is enough ventilation. Could you please post some photos of his tub that show the air holes?
As far as your temperatures, 88 degrees is much too warm for Bloods/Short Tails in my opinion. They definitely seem to prefer it cooler. I recommend 82 - 85 (at most) on the hot side and 75 - 78 on the cool side. The base temperature on the hot side for my Bloods/Short Tails is 82 degrees, but inside of their hides it's usually around 83 - 85 degrees.